Abstract : This paper summarizes three years work on blunt probe theory and experiments in the low ionosphere, during which time sixteen rocket launched parachute borne blunt probe experiments were conducted. Detailed studies of the viscous boundary layer flow about subsonic blunt probes show that they collect charged particles by a simple mobility mechanism. This is also true for d.c. probes in the supersonic regime provided the reduced mobility is constant. A.c. operation of blunt probes provides a means of measuring the mobilities and relative abundance of charged particle constituents. (Author)